Field of the Invention
The invention concerns a method to acquire magnetic resonance data as well as a magnetic resonance system and an electronically readable data storage medium to implement such a method.
Description of the Prior Art
Magnetic resonance (MR) is a known modality with which images of the inside of an examination subject can be generated. Expressed in a simplified manner, the examination subject in a magnetic resonance apparatus is positioned in a strong, static, homogeneous basic magnetic field (called a B0 field) with a field strength of 0.2 to 7 Tesla or more, such that nuclear spins in the subject orient along the basic magnetic field. Radio-frequency excitation pulses (RF pulses) are radiated into the examination subject to trigger nuclear magnetic resonance signals that are detected and entered in an organized manner as data points in an electronic memory known as k-space. On the basis of the k-space data, MR images are reconstructed or spectroscopy data are determined. Rapidly switched magnetic gradient fields are superimposed on the basic magnetic field for spatial coding of the measurement data. The acquired measurement data are digitized and stored as complex numerical values in a k-space matrix. For example, by means of a multidimensional Fourier transformation, an associated MR image can be reconstructed from the k-space matrix populated with values.
In the acquisition of magnetic resonance data for imaging, MR from the subject (or volume thereof) to be imaged must be acquired completely in all phase coding directions in order to avoid aliasing artifacts. Particularly in three-dimensional acquisition techniques, which use two phase coding directions for the spatial resolution, the flexibility in the adjustment of the parameters to be used in the acquisition is thereby reduced, or the duration of the acquisition is increased, thereby reducing the desirability of such acquisition techniques in everyday clinical settings.
Often techniques known as “oversampling” techniques, in which additional data are measured (acquired) in the phase coding direction but are discarded in the reconstruction, have been used to avoid aliasing artifacts. However, the measurement time is thereby increased (drastically in some circumstances), which can also lead to problems with the permitted specific absorption rate (SAR).